1) Field of the Invention
The present invention relates to an image pickup device and image pickup method. More particularly, this invention relates to a digital image pickup device.
2) Description of the Related Art
Most digital cameras as digital image pickup devices include an internal flash. It has been known that an image obtained by photographing a subject by a digital camera using a flash from a relatively short distance tends to be overexposed. The invention described in Japanese Patent Application Laid-Open Publication (JPA) No. 2000-278598 has been achieved to correct image data which is likely to be overexposed to thereby obtain an adequate image.
According to the invention described in JPA No. 2000-278598, a γ correction table is created. This table corresponds to a converted curve obtained by shifting the lowest luminance of an input signal in a reference conversion characteristic curve (which is used for γ correction) to the lowest luminance of an obtained input signal. The image data which is likely to be overexposed is processed by the conversion table thus created, whereby the unevenness of output image signals is corrected.
However, it is known that photographing using a flash by the digital camera has not only an overexposure problem explained above but also a problem that a picked-up image has uneven luminous intensity distribution. The uneven luminous intensity distribution is a phenomenon that occurs because of a long distance between an optical system and a flash in the digital camera. This phenomenon becomes more significant as a distance between a subject and the digital camera is shorter.
If a subject is photographed using a flash at a short distance by the digital camera, the quantity of light around an image is sometimes decreased by the shading of the optical system in the digital camera. In this case, the phenomenon as follows occurs. That is, the peripheral portion of the picked-up image darkens or the brightness of an image frame becomes uneven, and this phenomenon may possibly degrade the image. If the light quantity of the flash is increased to solve the problem of darkening of the peripheral portion of the image, a phenomenon of halation which causes any white void to appear in image processing, may occur in the central portion of the picked-up image frame, which may possibly degrade the image.